1. Field of the Invention
The present invention relates to a rolling bearing.
2. Description of Related Art
An angular contact ball bearing is known as a bearing that supports rotating shafts of various mechanical apparatuses. In recent years, the rotating shaft of such a mechanical apparatus is often rotated at high speed in order to improve machining efficiency and operational efficiency. Thus, high reliability of the angular contact ball bearing has been demanded; for example, the angular contact ball bearing needs to be protected from seizure at high rotation speed. In an increasing number of cases, grease lubrication, which exhibits high lubrication performance, has been adopted instead of oil lubrication in which a lubricant is supplied to the inside of a bearing, in order to improve the reliability of the angular contact ball bearing. In the grease lubrication, the grease is pre-contained inside the bearing.
The grease contained inside the bearing needs to be supplied to portions that need lubrication during operation of the bearing. Thus, various proposals have been made to improve the flowability of the grease inside the bearing (see, for example, Japanese Patent Application Publication No. 2010-164122 (JP 2010-164122 A)).
In an angular contact ball bearing 30 described in JP 2010-164122 A, an inner ring 31 has an angular shape as depicted in FIG. 5. That is, with reference to an axial direction (lateral direction in FIG. 5), a right shoulder diameter and a left shoulder diameter are different from each other. Specifically, in FIG. 5, the shoulder diameter of a right area 32 of the inner ring 31 is larger than the shoulder diameter of a left area 33 of the inner ring 31. A circular arc surface joining the areas 32 and 33 together defines an inner ring raceway groove 34.
In the angular contact ball bearing 30, an outer ring 35 has a deep groove shape, as depicted in FIG. 5. That is, with reference to the axial direction, the right and left shoulder diameters are the same. Specifically, in FIG. 5, the shoulder diameter of a right area 36 of an outer ring 35 is substantially the same as the shoulder diameter of a left area 37 of the outer ring 35.
Grease storage grooves 39a and 39b leading to a raceway groove 38 of the outer ring 35 are formed in an inner peripheral portion of the outer ring 35. The grease storage grooves 39a and 39b are each formed outside the raceway groove 38 in the axial direction. In FIG. 5, a grease guide surface 40 inclined inward in the axial direction and outward in a radial direction is formed in a groove wall of the grease storage groove 39b, located on the right in FIG. 5.
In the angular contact ball bearing described in JP 2010-164122 A, grease collected in the grease storage groove 39b during operation is pressed against the grease guide surface 40 by a wind pressure caused by rotation of a cage 42 resulting from rolling of a ball 41. The grease pressed against the grease guide surface 40 is stably fed to the raceway groove 38 of the outer ring 35 along the inclined grease guide surface 40.
However, for example, the inner ring 31 has the angular shape and a pump effect is exerted in which the ball 41 spins during operation, and thus, the grease is disadvantageously likely to concentrate at one side (on the right in FIG. 5). The grease concentrated at the one side may be retained in place or may even leak to the exterior through a labyrinth at a leading end of a noncontact seal 43. The retention or leakage of the grease leads to inappropriate lubrication, resulting in defects such as seizure, temperature elevation, or wear.